Reaching time synchronicity between a transmitter and a receiver under inter-symbol interference conditions may be difficult, and sometimes even impossible. Timing recovery mechanism at the receiver may not work correctly, or alternatively lock in a wrong steady state condition in presence of inter-symbol interference. Some receivers employ an equalizer aimed at reducing inter-symbol interference. The equalizer is often used in conjunction with a timing recovery mechanism, wherein both the equalizer and timing recovery mechanism try to converge to a correct steady state operation simultaneously. Simultaneous convergence into a correct steady state operation may be either impossible or not produce deterministic results due to inter-dependencies between the equalizer and timing recovery mechanism.
A good equalization solution may include an analog equalizer, a digital Feed Forward Equalizer (FFE), and a digital Decision Feedback Equalizer (DFE), working simultaneously with a timing recovery loop mechanism performing frequency and phase errors corrections. Inter-symbol interference may be partitioned into pre-cursor inter-symbol interference, and Post-Cursor inter-symbol interference. The analog equalizer and FFE are capable of correcting both types of inter-symbol interference, while the DFE is capable of correcting only Post-Cursor inter-symbol interference. Twisted-pair and coaxial communication links typically have low-pass frequency characteristics, resulting in equalizers having high-pass frequency characteristics.
Other common impairments in wire-based transceivers are cross talks and echo, which tend to have high pass characteristics. Analog-to-Digital converters sample received signals as well as noise, which is aliased into the receiver bandwidth in addition to the received signal.